By Kevin Sabet, Special to CALmatters

“One last drink for the road,” once a widely-used phrase, is thankfully out of vogue now, as we have learned the painful lessons of drinking and driving.

And though science has shown that another intoxicant – marijuana – should be added to the list of no-nos while driving, not everyone has gotten the message.  State Controller Betty Yee and her husband were unfortunate victims of California’s lax attitude toward pot.

They were rear-ended on July 13 by a driver who allegedly was high on marijuana. Although everyone survived, this incident brings into focus the facts of marijuana-impaired driving.

A recent study out of Washington state found that almost 17 percent of marijuana users admit to using the substance every day. More than half of daily users aged 15 to 20 believe marijuana made them better drivers. Science says otherwise.

The National Institutes of Health reports that marijuana’s active ingredient – THC, which is more potent now than ever—can impair a driver’s reaction time and ability to judge time and distance.

Numerous studies have shown that marijuana use can make it difficult for drivers to stay in their lanes and pay proper attention to the road. These studies also noted that when marijuana was used in conjunction with alcohol, which is becoming more common, impairment levels are further increased.

In Colorado, the first state to legalize pot, the number of drivers intoxicated with marijuana and involved in fatal crashes increased almost 90 percent from 2013 to 2015.  Further, over 76 percent of driving under the influence of drugs charges in Colorado involve marijuana.

According to the Fatality Analysis Reporting System, about 40 percent of drivers who were killed in car crashes and tested for drugs tested positive for some form of marijuana.

While the data show that marijuana-impaired driving is an increasing threat to public health, law enforcement is finding it difficult to enforce drugged driving laws.

Prophetically, Yee opposed Proposition 64, the 2016 initiative that legalized marijuana in California, on the grounds that she did not believe the state had the proper infrastructure in place to best regulate the new industry.

Among the lacking regulations: a roadside test that could adequately gauge marijuana impairment. Unlike alcohol, higher THC levels do not always coincide with higher levels of impairment and vice versa.

A person can be under the influence of marijuana and clearly show signs of impairment, yet only have a low amount of THC in their blood, particularly after ingesting pot candies or other edibles.

The Denver Post recently found that marijuana-impairment may be underrepresented in current data because testing for it is more expensive than testing for alcohol.

There is a definite need for a better system to allow police departments to be able to keep marijuana-impaired drivers off our roads. But one of the easiest ways to keep from exacerbating this problem would be to pump the brakes on the rush to legalize, promote, and commercialize marijuana in California and beyond. Cities and counties should be encouraged to exercise their rights to ban pot shops in their communities.

The crash involving Yee is a canary in the coal mine.  The dangers of drugged driving are real. Three women in California were killed by a driver high behind the wheel just a few months ago. In May, West Virginia Gov. Jim Justice was in a car hit by a stoned driver. They were lucky that there were no injuries in that crash.

We need a real conversation about the dangers of pot and driving now – driven by science, not pot industry rhetoric – before more people are hurt.

Dr. Kevin Sabet served as a drug advisor to three presidential administrations and is founder and president of Smart Approaches to Marijuana, [email protected] He wrote this op-ed for CALmatters.